A computer system backplane typically comprises a plurality of conductive layers held rigidly in spaced parallel relation by an interleaved plurality of dielectric layers. While a given dielectric layer has equal significance with respect to the two conductive layers flanking it, one sometimes finds it convenient to conceptualize the backplane as comprising a plurality of coextensive circuit board layers laminated to one another, each layer being of composite construction, including a conductive layer and a dielectric layer. The backplane carries a plurality of parallel multi-terminal sockets that receive in an edgewise manner the circuit boards (called "plugboards") on which the computer system components are constructed. Some of the backplane conductive layers are used for signal propagation, and comprise a relatively large number of separate conductive traces running between the parallel transverse sockets. Others of the conductive layers are so called power planes that provide the fixed voltage levels necessary for system operation, and are generally in the form of solid sheets of conductive material (typically copper).
Each socket includes a large plurality of pins that pass through small plated holes bored through all the layers and make electrical contact with a desired one of the backplane conductive layers. Where connection to a given layer is not required, a region surrounding the hole through that particular conductive layer is insulated to prevent the pin from making contact. The plated holes are sized relative to the connector pins for a press fit.
Power supply connections are made in a generally similar manner, but on a larger scale. For example, the plated bore for the power plane connection is of a diameter typically on the order of a quarter inch in diameter, and a solid wire of comparable diameter is smoldered in.
It will be appreciated that current is supplied to or drawn from the power plane over a relatively small area, leading to relatively large local current densities. Accordingly, while the prior art power distribution systems tend to be suitable for currents of the order of 20 amps, they are not suitable when it is desired to supply considerably larger currents (perhaps 500 amps).